Sort part list when inspecting vehicle.

When examining a vehicle, installed parts are shown with structure first like before, then the rest of the parts are roughly sorted from top (solar panels, mounted guns) to bottom (wheels). Fixed the problem that parts would appear randomly in the list based on the order in which they were installed.

Passing the veh parameter is a bit clunky, but since the vector contains ints I didn't see a good way to do it. Suggestions for improvements welcomed.